Localising the gamma-ray emission in Flat Spectrum Radio Quasars and an extragalactic population study for the Cherenkov Telescope Array

This thesis is concerned with localising the gamma-ray emission region in Flat Spectrum Radio Quasars (FSRQs) and assessing the extragalactic source populations that will be detectable with the Cherenkov Telescope Array (CTA). An analysis of the gamma-ray flux from the nine brightest FSRQs detected with the Fermi-Large Area Telescope (LAT) during its first 8 years of operation is undertaken. Three different methods are employed to constrain the location of the emission region during identified flare periods, namely, measuring the shortest variability timescales, searching for evidence of a cut-off in the spectra and investigating the energy dependence in cooling timescales. Monte Carlo simulations are then implemented to constrain the very high energy (VHE) photon emission from the sample during the entire observation period. The combined findings of all the approaches suggest that the gamma-ray emission in the brightest FSRQs originates in multiple compact emission regions throughout the jet, within both the broad-line region and the molecular torus. The remainder of this thesis describes a detailed investigation of the extragalactic AGN sources that will be detectable with the CTA when in operation. The spectra from a sample of 1551 Fermi-LAT detected AGN having a known redshift measurement are extrapolated to the energy range 30 GeV - 200 TeV and the detection significance for each source is obtained using the anticipated instrument response of the CTA. The results reveal that the CTA will detect over 300 sources in 20 hours of observation and a list of promising candidates from each AGN class is presented. The improved statistics will allow a range of scientific topics to be explored including obtaining a reliable estimate of the luminosity function in the VHE regime for the first time. A preliminary evaluation of the evolutionary parameters using the expected CTA blazar source count distributions is discussed in this thesis.